One gun color-dot tube with dynamic beam convergence



July 3,1, 1956 R. R. I Aw 2,757,231

ONE: GUN coLoR-DoT TUBE WITH DYNAMIC BEAM coNvERcENcE Filed June l. 19502 Sheets-Sheet 1 Qkbwb wl: W N wwwwmm mL m .ESN /mm Qbkuxbwmw N .MASS NA H@ ,w w n@ f Nm .w M w YHQ WGQ .fl mm, Q T M f QR .Ss w Q.nm mm w R Sm f m. mw w m (NN f-: i SSG w S. Q mwwmm E e ww |V @SNS k w. NN QN N. mSw T vm m N Img .mdmx k/ b,

July 31, 1956 R. R. LAW 2,757,231

ONE GUN COLOR-DOT TUBE WITH DYNAMIC BEAM CONVERGENCE Filed June l. 19502 Sheets-Sheet 2 INVENTOR Ru el] R.Law

United States Patent O il it.

UNE GUN COLOR-DGT TUBE WITH DYNAIVIIC BEAM CNVERGENCE Russell R. Law,Princeton, N. J., assigner to Radio Corporation of America, acorporation of Delaware Application June 1, 1950, Serial No. 165,551

The terminal years of the term of the patent to be granted has beendisclairned 1o Claims. (c1. 17e- 5.4)

This invention relates to electron beam-controlling systems. Though notnecessarily limited thereto, it has particular reference to Icontrolsystems for effecting electron beam convergence in multi-colorkinescopes.

The problem of controlling the convergence of a plurality of electronbeam components at substantially all points in the plane of a targetelectrode over which they are delected to scan a predetermined raster isone which frequently is encountered in television image-reproducingsystems. The trend toward providing kinescopes with flatter screens hasmade the problem of achieving beam convergence more severe. In certaintypes of kinescopes used in color television systems, the particularproblem is to elTect accurate convergence of a plurality of electronbeams, or their equivalents, which are directed tov/ard a targetelectrode from different angles. The different angles of approach of theelectron beams are employed for color selection purposes.

A representative multi-color kinescope of the type in which colorselection is eected by the angle of approach of an electron beam formsthe subject matter of a copending U. S. application of Alfred N.Goldsmith, Serial No. 762,175 filed July 19, 1947, now Patent No.2,630,542 issued March 3, 1953 and titled Multicolor Television. TheGoldsmith tube has a luminescent screen consisting of a multiplicity ofphosphor areas of sub-elemental dimensions. The phosphor areas arecapable respectively of producing light of diiferent colors when excitedby electron beam components. The different screen areas are scanned byelectron beams produced by a plurality of guns and projected toward thescreen through an apertured masking electrode. The desired colorproducing phosphor areas are selected by the angle at which the electronbeams traverse the apertures of the masking electrode.

Another multi-color kinescope with Which the present invention may beemployed successfully forms the subject matter of a copending U. S.application of Russell R. Law, Serial No. 165,552, led .lune 1, 1950 andtitled Color Television. The Law tube has luminescent screen andmasln'ng electrode structure similar to that embodied in the Goldsmithtube. It also operates on generally the same principles. The chiefdifference is in the provision of only a single electron gun. Theelectron beam produced by this gun is caused to approach the maskingelectrode and the luminescent screen from dilerent angles by imparting aspinning type of movement to the beam. By such means the electron beamis caused to rotate about the center or longitudinal axis of the tube sothat, at successive intervals, it occupies substantially the samepositions as those occupied by the separate electron beams in theGoldsmith tube.

The expression electron beam components as used in vthis specificationis intended to cover the type of phosphor-exciting electronic energyproduced by a single or a plurality of electron gun. This energy may becontinuous or pulsating as required without departing from the scope ofthis invention.

l i 2,757,231 Patented July 31, V1956r It is necessary for thesuccessful operation of multicolor kinescopes of the type represented bythe Goldsmith and Law tubes referred to that the plurality of electronbeam components be made to converge substantially in the plane of themasking electrode at all points in the raster or other predeterminedpattern scanned thereon by thedeection of the beam components. In orderto accomplish this, it is necessary to provide a dynamic convergencecontrol of the electron beam components. One such electron beam controlsystem forms the subject matter of a copending U. S. application ofAlbert W. Friend, Serial No. 164,444 led May 26, 1950 and titledElectron Beam Controlling System. In this Friend application there isprovided an electron-optical system which is variably energized as afunction of both the horizontal andl vertical deections of the electronbeam components. Further details or dynamic beam convergence system maybe found in a paper titled Deection and Convergence in Color Kinescopesby A. W. Friend, published in the Proceedings of the I. R. E., vol. 39,No. 10 at page 1249. The present invention is in the nature of animprovement upon the Friend system, particularly in color televisionsystems of a particular character.

The present invention is particularly adapted for use with a colorkinescope embodied in a color television system operating in accordancewith the dot or elemental multiplex principle. A system of such acharacter forms the subject matter of a copending U. S. application ofJohn Evans, Serial No. 111,3 84, tiled August 20, 1949 and titled ColorTelevision. information from each elemental area of the televisionsubject is transmitted bysuccessive video signals; The composite videosignal wave which includes all of the color information from all of theelemental areas in succession of an image to be reproduced is sampled ata receiving point. The rate at which the video signal sampling iseiected is equal to a multiple of the rate at which the elemental areasof the image are to be reproduced. The particular multiple depends uponthe number of component colors in which the image is to be reproduced.Ordinarily color television systems employ three compo? nent colors. Inthis case the video signal wave is sampled at the third harmonic of theelemental area repetition frequency.

It is an object of the present invention to provide animproved electronbeam control system by which to effeet convergence of a plurality ofelectron beam compo- The invention is embodied in Van electron-opticalsys-y tem for effecting convergence of a plurality of electron beamcomponents. The system is energized variably in4 accordance with thedeflection of the beam components.

The energization of the system also is varied at a fre-` quencysubstantially higher than the horizontal dellection frequency.Preferably, this higher frequency corresponds to the elemental imagearea repetition frequency. In al color television system, it may beequal to the frequency;

at which a composite multiplex video signal waveis sampled.

The novel features that are. considered characteristic of this inventionare set forth with particularity in the appended claims.V The inventionitself, however, both'l as to its organization and method of operationas Well In this type of system, the color as additional objects andyadvantages thereof will best be under-stood fromthefollowingVdescription takerr in- In the drawings: f f

Figure` 1A is` a circuit diagram mostly' inf block. form of' a colortelevision" signal receiver and 'image-reproduc ing@ system embodyingthe invention; f

f connection` with the accompanying drawings.

4. subjected to the influence of a rotating field produced ,by ai coil-2'1 surrounding theneck of the tubef substantially. as shown.y y Thiscoil is energized by a constantly changingvoltage of a charactery toyproduce a rotating field by means of ywhich the electron beam iscaused. to

f spin or rotatefabout the centraly longitudinal axis. Such Figure 2 isasectional view of a portion' of 'a` color f kinescope used inthe systemof .Figure 1, taken on the lines 2-'-Z of Figure 1'. The present'figure' shows" the general configuration and relative 'positioning ofthe com-y ponents1 ofA the electronLoptical; system for effectingdynamic'electron beamV convergence;

kapparatus yis of the same general` type as that shown in yPatent2,057,773issued October 20; 1936 to W. G. H.

, Finch.,

` Figures r3, 4, and1 5A areviews of thekinescope screen;

f Figure 3 indicatesy the non'-convergen'c'e of the electron beamcomponents inthe absence of any dynamic convergence control;

Figure 4- indicatesarst order improvementy ofelectrolr' beam'convergence byproviding dynamic` beam con yvergencc. control varying asa function of horizontal and vertical beam#- deflections; 'and Figure 5illustrates a` secondorder improvement of f electron-"beam, convergencein which-.the dynamic con'- vergence control` system is varied furtherasr a function of' the1 video signal: wave' sampling frequency kinaccord`r k a'ncewith this invention;

Reference r'st will be made to Figure ,1' yof"the-'drawrings. Thetelevision signal-receiving or image-reproducyingfsystem show-n in blockdiagramformgenerally iscon-y ventional.' An antenna 11 'iscoupled toyyacompositeL impressed upon a synchronizing signal separator'14;apparatus. also. may be` entirely conventional. Ac-

cordingly, it. will be understood that. it includes `appay ratusz` for(separating the ksynchronizing signalsA fromv the video signals. Also,the horizontal synchronizingfsignas are: separated from the verticalsynchronizing signals.

The image-reproducing apparatusalso` includes a kine scope which, forillustrativelpurposes, isIof thekind disclosed in. the. copending` Lawapplication referred to. Such. a` kinescope a1so:is;disc1osedV inl apaper titled A- One-Gun Shadow-Mask: Color. Kinescope by R..R. Law;published in the Proceedings of the I. R. E., vol'. 39, No. 10, October19.5:1 at page' 1194; Essentially, it includesl a. luminescent screen16, an aperturedf masking electrode 17 and an electron gun 18. The'.luminescent screen- 16 may be formed on'. a substantially flattransparent plate. The phosphors are disposed on thefinsideA surface;ofthe plate in any.` desired pattern'. Preferably, multi-coloredphosphors` are in. the formof. sub-elementall areas or, dots. arrangedin4 groups.y Each` group of. phos-f phor dots contains at leastr oneeach of' phosphors` capa.- ble` ofrespectively producing lightl. of the:component image colors. The masking electrode` 11 is. provided; withamultiplicity of apertures. 'Ihese` apertures are provided in the same.patterni as the groups.: of phosphor dots. appearing upon the screen I6.Each. aperture of theelectrode 17 is: in-registrationewitlr one group ofphosphor dots.

The` kinescope` 1'5- also. is: provided' with` a deecting yoke 1-9 ofsubstantially conventional'V form'. It' will be understood that theyoke, when; suitably energized, functions todeflect the electron. beam.components over the masking. electrode surface in` accordance withl apredetermined. pattern. or' raster.`

In. this case, the plurality of.' electron beam components is derivedfrom a single electron gun 18. Tliisgun is .mounted in sucli a; mannenthattheelectron'. beam emanating therefrom is" substantially along. the,centralV longitudinal ,axis ofthe kinescope. The electron bea-mis "[le.kinescope, 15- also; is provided with: a magnetic yconvergence coil 22.This coilisenergized to-produce a steady or static iield` of a characterto cause the spinning electron beam to impinge upon ya pointofthemaskingy electrode 181 located substantially at the center.` thereof ina the absence of` any energizaticm4 ofthe'deecting yoke 19. Such a coilisfof the same generalr character as a beam focusing coil, an example ofwhich is disclosed in Patent 2,442,975 issuedlune 8, 1948 to G.LGmndrnann. y

The magnetic" convergence coil 22` is ,energizedA from'r a powersource,l indicated; yby* a; batteryr 23' throughy a rheo-r stat 24. Bysuitable' adjustment ofy the rheostat the spinning` electron beam may bemade to impingeupon the' center of theY masking electrode 17,irrespective of its radial location relative to" the' central axis ofthe' tubei kThe color rkinescopey 15j` alsol is kprovided with an elec-`tron-optical systemby kWbichtoy effectV convergence of y rthe electronbeam components at substantiallykr all kpoints in the yrastery scannedin-y thej planeof the ,maskingyele'cif trode`17kr As disclosed rhereinfor illustrative purposes, the` electron-optical ysystemcomprisesi-ayvertical dynamic convergencev coil 25 yand' a horizontal;`dynamic converg--Ay ence coil 261. Theshapeofeach of theseitwoK collsis`substantially el1ipn generally ellipticalv so as to provide tical orcylindricalelectron lenses. Further details, of

" such` coils may ,beV foundin the Friend I; R. EL'paper previouslyreferred to,y particularly in-tlie ydescription of Figure 2.1y of thatpaper., n n

` Thecontrol circuits for the' color kinescope, 15 ralsm includes theusual deflection generators y2.7 coupled 'for-r 'control tothesynchronizingfsignal separator 111;'k The", koutput ofthe deflection'generator, which willl be understood to`- produce substantiallysawtootli waves; at horizontal or vertical frequencies respectively, iscoupled; to thedetleeting yoke 19. In thisl manner the deectmgfieldsproduced by the yoke causethe electron beam com-` ponents to scantheAvtarget electrode structure-1n a` pre1- determined pattern.

The sampling of the composite videof signalv wave as.` disclosed herein`is in accordancewith the soacalled-high: levelV samplingI principle. Asystem of suchsignal sarnplirlg' forms` the subject matter of acopeudingU. Si application of George C. Siklai, Serial No'.` 145,4.20,` filedFebruary 2l, 1950, and titled Color Televislon. Receiving/System Ahigh-level? videosignal sampling systemconsists generally of" asinglevideo signal. amplier channel in which= the v-ideo' signals representingall of` the component colors are; amplied= simultaneously. rEheamplified composite video signal is impressed upon oneV of a pair of`electronbeam` intensity control electrodes of the color kinescope; Theintensity control electrodes normally are biased relative to one anotherso thatno electron` beam; isproduced The other intensity control"electrode is keyed concurrently with the reception off successive color'representative video signals; rIhe keying of the electron gun producesAan electron'beam. The intensity of the electron `beamuislcontrolled inaccordance'with the amplitude of thevid'eosignal Wave'rcceived` at thatinstant. lt, therefore, isseen that it is necessary tokey the-electronbeanrefi the-colorkinescope at|` a` fre'- quency corresponding totth'erepetition frequency of the video signals. InA a tlireewcolor televisionsystem this repetition frequency' is three times tliev frequency; atwhich' the successive elemental'l areas of the: image' are` reproduced.

Accordingly, thel presenti4 apparatus includes a sampling frequencyoscillator 28 coupled for synchronizing control to the synchronizingsignal separator 14. The essential requirements of an oscillator bywhich to control video signal Wave sampling are that it be relativelystable at a frequency equal to the frequency at which the elementalareas of an image are to be reproduced and that it be susceptible ofsynchronous control from an external source. An oscillator of thecharacter described is disclosed in the book entitled Wave Formspublished by McGraw Hill Inc., New York, at page 143 with particularreference to figure 4-45. The output of the oscillator 28 is essentiallya sine wave at an elemental dot frequency of the television image. Theoutput circuit of the oscillator 28 is coupled to a frequency multiplier29. In the case of a three-color television system the frequencymultiplier increases the fundamental frequency produced by theoscillator by a factor of three. The frequency multiplier is coupled tothe electron gun 18 as indicated to control the keying of the electronbeam in the manner described. The sampling frequency oscillator 28 alsois coupled to a rotating iield generator 31. This device is coupled tothe magnetic convergence coil 21. It is considered that means forproducing constantly rotating magnetic fields are so well knowngenerally, as indicated in said Finch Patent 2,057,773, that it is notnecessary to disclose a particular one here in order to completelyunderstand this invention. Accordingly, it Will be understood that thegenerator 31 includes means for producing substantially sinusoidal wavesof such a character that, when impressed upon the coil 21, there areproduced rotating magnetic fields that are always substantially 180 outof phase with one another.

The electron-optical system including the coils 25 and 26, by whichdynamic convergence of electron beam components is effected, isenergized as a substantially parabolic function of the horizontal andvertical deiiection of electron beam components. Accordingly, thevertical dynamic convergence coil 25 is variably energized by a waveproduced by a vertical convergence control wave generator 32. It will beunderstood that this generator 32 includes suitable wave shapingcircuits to produce a wave of suitable form to energize the coil 25 inresponse to signals derived from the deflection generator 27 at thevertical deflecting frequency. A convergence control wave ofsubstantially parabolic form may be produced by a suitable integrationof a sawtooth wave as taught in Patent 2,312,054 issued February 23,1943, to O. H. Schade. In general, the energization of the coil 25 is aminimum when the-electron beam components are directed at pointssubstantially at the center of the vertical scansion of the targetelectrodes. The energization of the coil 25 increases in suitablepolarity as a function of an increase in the angle of deflection'of thebeam components from the central vertical portion of the raster.

The horizontal dynamic convergence coil 26 also is energized by a wavederived from a horizontal convergence control wave generator 33. Thisapparatus, except for values of the circuit components, may besubstantially similar to the generator 32 and may follow the teachingsof said Schade Patent 2,312,054. In this case, however, it is requiredto produce waves of suitable substantially parabolic shape at thehorizontal deflection frequency. The output of the generator 33 iscoupled to the control grid 34 of an electron tube 35. This tubefunctions as a signal-combining stage by which to develop a compositecontrol wave for impression upon the coil 26. The anode of the tube 35therefor is coupled to one terminal of the coil 26. The other terminalof the coil is connected to the positive terminal of a power supplyindicated at -l-B.

The vertical and horizontal convergence control wave generators 32 and33 may be of the general type disclosed in greater detail in Figure20,`and related description thereof, of the previously referred toFriend I. R. E.

6 paper. The outputs of these generators may be coupled to theconvergence coils as indicated in Figure 1 of the drawings herein.

In accordance with a special feature of the present invention a wavecomponent having the fundamental frequency of the sampling frequencyoscillator 28 is combined with the output from the wave generator 33.For this purpose the output of the oscillator 28 is coupled through aphase adjuster 36 to a primary coil 37. A secondary coil 38 isinductively coupled to the coil 37 and is connected between a source ofpositive voltage and the screen grid 39 of the tube 35. Manipulation ofthe phase adjuster 36 results in the impression of a voltage componentat image dot frequency upon an input electrode of the tube 35 insuitable phase to combine effectively with the wave derived from thegenerator 36 so that an improved dynamic convergence of the electronbeam components may be effected by the coil 26.

A graphic illustration of the effectiveness of the system embodying thepresent invention as given in the Figures 3, 4 and 5 to which referencenow will be made.

In Figure 3 the color kinescope is provided with no dynamic convergencecontrol. The central trace 41 is one which is made by a spinningelectron beam of the character described. By suitable adjustment of therheostat 24 the magnetic convergence coil 22 may be energized toconverge the spinning beam to a point 42 at the luminescent screen 16.It may be seen from an inspection of the figure that, as the electronbeam is deilected both vertically and horizontally from the centralposition, the convergence of the beam components is subject to arelatively wide variation. For example, the trace 43 located at oneextreme of a horizontal deliection of an electron beam no longer issubstantially a point as it is at the center of the raster.

It may be appreciated that a spinning beam following a path such asindicated by the trace 43 will produce a misregistration of the electronbeam components with the different color-producing phosphor areas of thescreen 16. The failure of the beam components to converge any betterthan indicated by the trace 43 will result in such a degradation of thereproduced image which can not be tolerated. It may be seen from Figure3 that the tendency of the beam components to fail to converge is muchgreater in a horizontal sense than in a vertical one.

The electron beam traces at different points of the raster as shown inFigure 4 represents the improved operation of a color kinescope whendynamic convergence control means are provided. The dynamic convergencecoils 25 and 26 are energized by waves varying in accordance withhorizontal and vertical deflection frequencies. However, no energizingcomponent at the dot repetition or sampling frequency is present in thecontrol wave for the dynamic convergence coils. The conditions toproduce the results of Figure 4 may be simulated by impressing aconstant potential upon the screen grid 39 of the tube 35 of Figure 1.

Figure 5 represents the added improvement in the dynamic convergence ofthe electron beam components when the sampling frequency component isincluded in the control wave for the horizontal convergence coil 26.

It will be appreciated that alternatively in accordance with thisinvention, a sampling frequency component may be introduced in thecontrol wave for the vertical convergence coil 25. Also, it will beunderstood that the present invention may be used successfully withplural electron gun tubes of the type covered by the Goldsmithapplication referred to. Furthermore, convergence coils 25 and 26 may becombined into a unitary structure which is not necessarily of ellipticalshape without departing from the scope of this invention.

Having thus disclosed the nature of the invention, its scope is set outin the appended claims.

What is claimed is: l. In a cathode ray tube image reproducing systemwherein. a plurality of electron: beam components effectivelytraversingzpaths spaced, respectively,` about a longitudinal axis of thetube are deected horizontally and vertically through substantially equalanglesv to' scan a raster in4 af predetermined plane, said` beamcomponents being differently deflected` at any instant by reason of saidtraversal of spaced paths, al dynamic convergence system to effectconvergence of said beam components at all.` points in` said rastercomprising, field-producing means` disposed'.L adjacentl to the'paths ofsaid beam components for producingV a' eld of suchcharacter as toconverge saidbeam components, means including a source of asubstantially parabolic Wave for energizing said field-producing meansin accordance with the angular deflection of said beamv components, andmeans effectively modifying, said substantially parabolic wave forvarying the energizationA of`saidliield p`roducing means-at a frequencyhigher than. that of said horizontal beam deflection.

2. A- dynamic electron beam' convergence system delined in claim l inwhich said field-producing means includes an electromagnetic coil systemfor producing both horizontal and vertical" field components and saidenergization varying means is of such acharacter that it operates tovary the energization of said field-producing means substantially at theelemental image area repetition frequency.

3. A dynamic electron beamA convergence system asV dened in claim 2 inwhich, saidenergizingrneans is of such a.` character that it providesenergy to vary the horizontal convergence field component at thehorizontal beam dellection frequency, and also energy to vary thevertical eld component at the vertical'beam deection frequency.

4: A dynamic electron beam` convergence system as dened in claim 3 inwhich, said energization varying' means is of such character that iteffectively varies only one'of said field components.

5. A dynamic electron beam convergence system asl defined in claim 4 inwhich, said energization varying means is of such a character thatitetfectively varies said horizontal field component.

6. In a color television system, a colorkinescope having a luminescentscreen comprising a multiplicity of groups of phosphor dots capable'respectively of producing light of different component colorsof an imagewhen impinged by electrons, anapertured masking electrode spaced behindsaid screen, said masking electrode having an aperture for, and insubstantial registration with, each of saidgroups of phosphor dots,means for directingl toward said screen a video signal-modulatedelectron beam, means for rotating said beam about a longitudinal axis ofsaid kinescope at a predetermined colorcycle repetition frequency,whereby toY cause components of' said beamto approach said screen fromdifferent' angles at successive instants ineach color cycle, means forangularly detlecting said beam to' trace a raster at said screen, saidbeam components being differently deected by reason of said beamrotation, a dynamic convergence system adjacent to the path of saidrotating beam and energizable to effect convergence of saidl beamcomponents at all points of said raster, means including a sourceof asubstantially parabolic Wavefor varying the energization of saidconvergence system-proportional to the angular deection` ofi saidi beamcomponents,- and means eectively modifying said substantially parabolicwave for varying the energization of saidconvergence system proportionalto saidcolor cycle repetition frequency.

7, In a color television"` system, a color kinescope having ayluminescent screen'` comprising4 a multiplicity of groups of phosphordotscapable respectively of producingV light of different component`colors of: an image whenimpinged by electrons, anv apertured mask-ingielectrode spaced behind said screen, said masking electrode" having anaperture for, and in substantial registration with, each of said groupsof phosphor dots, meanslfor directing toward'l said screen a videosignal-modulated electron beam; means for rotatingsaid beamlabout alongitudinal axisof, said kinescope` at` a predetermined color cyclerepetitionfrequency, whereby tocause components of said beam to approachsaidscreen through said masking; electrode from different` angles atsuccessive instants in eachf color cycle,.rneans1` for deilecting saidbeam horizontally and vertically to trace a raster at said screen, saidbeam components being differently deflected by reason of said beamrotation,` a dynamic electromagnetic convergence system surrounding` thepath of said rotatingz beam and` energizable to effect convergence ofsaid beam components at all points of said raster, means including asource of a substantially parabolic wave for varyingthe energization ofsaid convergence system at arate proportional to'the verticaldeflection'frequency, means including a source of a substantially parabolic wavefor varying the energization of said` convergence system at a rateproportional to the horizontal deflection frequency, and meanseffectively modifying` one of' said substantially parabolic Waves forvaryingv the energization of said convergence system at arateproportional tosaid color cycle repetition frequency.

8. In a` color television system, av color kinescope having ailuminescent screen comprising` a multiplicity of groups of phosphor dotscapable respectively of producing light of different component colors ofarrimage when impinged by electrons, an apertured` masking electrode`spaced behind said screen,` said masking electrode having; an aperturefor,. and in substantial registration with, each of said groups-.ofphosphor dots, means including` an electron gun for. directing towardsaid' screen a video signal-modulatedelectron` beam, means for rotating`said beamabout a longitudinal axis of said kinescope at a predeterminedcolor cycle repetition: frequency, whereby to cause components ofsaidbeamto approach said screen through saidv apertured` maskingelectrode from diiferent angles at successive instants ineach colorcycle, means for deflecting. said` beam horizontally and vertically totrace a raster at said screen, said beam components being differentlydeflected by reason of said beam rotation, a horizontall andverticaldynamic convergence coil system surrounding? the path of said, rotatingbeam and energizable` tor effect convergence of: said beam componente atalls points ofV said raster,` means including a source of a'.substantiallyl parabolic wave for varying the energization of said? coilsystem4 as a function of said vertical deiection` frequency, means'including a source of` a` substantially` parabolic` Wave: for varyingthe energization of saidcoil system as azfunction'of-,said horizontaldeection` frequency,` and. means effectively modifyingv one of said:substantially parabolic waves` for additionally varying the energizationof saidl coil; system as a function offsaid color cycle.` repetitionifrequency.

9. In a color television system, a color kinescope having a luminescent(screen` comprising a multiplicity of groupsofl phosphor dots capablerespectively of producingglight of different component colors of animage when impinged'by electrons,.a\masking electrodespaced behind saidscreen and; having an aperture for and` inregister with each'` of? saidgroups of phosphor' dots, means including an-` electron" gunfor'directing` toward said screen a videolsignal-modulatedelectron beam,means including al.rotatingeld-producing system for rotating said beamabout a.longitudinali axis of said kines'cope at a predeterminedcolorcycle repetition frequency, whereby to cause componentsof saidbeamtoapproach said-screenthrough the apertures ofi' said? maskingelectrode from different anglesat successive instants inV each colorcycle, means for deflecting said beam horizontally andi verticallyatdifferent frequencies to trace a raster at said screen, said beam".components being differently deected` by reason of said beam rotation,horizontal and vertical dynamic' convergence coils surrounding the pathofi said rotating. beanr and: energizable to effect convergence of saidbeam components at all points of said raster, means including a firstsubstantially parabolic wave generator for variably energizing saidvertical coil at said vertical deflection frequency, means including asecond substantially parabolic wave generator for variably energizingsaid horizontal coil at said horizontal deflection frequency, and meanseffectively modifying said substantially parabolic wave at horizontaldeflection frequency for variably energizing said horizontal coil atsaid color cycle repeti tion frequency.

10. In a color television system, a color kinescope having a luminescentscreen comprising a multiplicity of groups of phosphor dots capablerespectively of producing light of dierent component colors of an imagewhen impinged by electrons, a masking electrode spaced behind saidscreen and having an aperture for and in register with each of saidgroups of phosphor dots, means including an electron gun for directingtoward said screen a video signal-modulated electron beam, meansincluding a rotating field-producing system for rotating said beam aboutthe central longitudinal axis of said kinescope at a predetermined colorcycle repetition frequency, whereby to cause components of said beam toapproach said screen through successive ones of said apertures fromdifferent angles at successive instants in each color cycle, means fordeiiecting said beam horizontally and vertically at diierent frequenciesto trace a raster at said screen, said beam components being differentlydeflected by reason of said beam rotation, horizontal and verticaldynamic convergence coils surrounding the path of said rotating beam andenergizable to elect convergence of said beam components at all pointsof said raster, means including a vertical frequency substantiallyparabolic wave generator for variably energizing said vertical coil,means including a horizontal frequency substantially parabolic wavegenerator for variably energizing said horizontal coil, and meansincluding an oscillator producing a substantially sinusoidal wave havingsaid color cycle repetition frequency for variably energizing saidhorizontal coil.

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